The asymptotic decay of charge correlations in ionic fluids determines the capability of the system to perfectly screen an external charge over a finite length scale [1]}, [2]}.
In the vast majority of ionic conductors at thermal equilibrium, this screening is manifested either as a pure exponential decay of the fluid charge density distribution [3]} or as an exponentially damped oscillation that reflects a shell-like ordering of the charge carriers [4]}, [5]}, [6]}, [7]}.
A crossover between a monotonic and oscillatory behavior, in particular, is observed at decreasing temperatures and/or increasing ionic concentrations and takes the name of Fisher-Widom line [8]}. This picture is particularly suitable for describing the decay of the electrostatic potential of molten salts and ionic liquids in contact with planar surfaces [9]}, [10]} and provides the general groundwork for interpreting the nanoscopic nature of the screening lengths in concentrated water-electrolyte solutions [11]}, [12]}.
